Energy in Service Flashcards
(23 cards)
What are positives of nuclear fusion?
- Efficient conversion of mass to energy
- Abundant fuel supply
- No emission of greenhouse or other polluting gases
- No risk of a severe accident
- No long-lived radioactive waste
- But a working concept is yet to be demonstrated
What is fusion?
several nuclei fuse together and release energy. The repulsion between nuclei is overcome by increasing the speed or energy of D and T in a hot fusion of plasma so that D(Deuterium) and T(Tritium) are hot enough to fuse.
What are the hydrogen isotopes and their differences? Where are they from?
Hydrogen out of water, (1 proton with 1 e- in shell)
Deuterium out of sea water (1 proton, 1 neutron and 1 e- in shell)
Tritium out of fusion (1 proton, 2 neutrons and 1e- in shell)
What is a tokamak reactor? key components
Key components:
[ref pg 26]
poloidal field coils, first wall/blanket, cryostat, radiation shiled, divertor, vacuum vessel
* Energy from fusion reactions are radiated to the first wall and blanket and
converted to heat.
* Hot blanket and first wall is cooled
* Thermal energy is extracted from coolant for power generation.
What is the fusion blanket?
Radiation is produced from the plasma to the first wall into the ‘blanket’. The blanket is made up of the tritium breeding zone(AKA helium=lithium + neutrons) and coolant for energy conversion. There is a shield next then a vacuum vessel and magnets finally. The plasma could be 150 million deg C.
What is the basis of radiation damage?
A free neutron can hit an atomic lattice and displace the atoms from their position e.g vacancy. Sometimes the neutron can bounce off an atom and hit another atom(known as a collision cascade from particle irradiation on metallic lattice) in the lattice just as the same atom that is displaced can displace other atoms e.g interstitial (in wrong place).
Interaction of energetic neutron particles with crystal lattices
Primary knock-on atoms (PKA)
+ point defects (vacancies,
self interstitial atoms)
atomic displacement cascades
secondary knock-on atoms
How can the measure of radiation damage be completed?
- Recombination of vacancy-interstitial atom pairs
99% of these displaced atoms eventually recombine to annihilate both defects.
The final microstructure results from a balance between radiation damage and thermal annealing.
The initial primary defects that escape in-cascade recombination undergo long-range diffusion and thus changes the material’s microscopic and macroscopic properties. - Displacements per atom (dpa)
Measure of radiation damage in irradiated materials
The number of atoms that could possibly be permanently displaced from their lattice site positions to stable interstitial sites.
1 dpa means that during irradiation in the average each atom was displaced once
Why does radiation damage matter?
- Radiation damage drives complex microstructural
and micro-chemical evolutions - Material properties are all largely determined by nature of their defect structure
There can be vacancies, voids, edge dislocations, dislocation loops (vacancy or interstitial type) etc [ref pg 35]
How does radiation damage emanate in the materials microstructure?
- Small defect clusters
- Dislocation loops
- Stacking fault tetrahedra
- Precipitates
- Voids (large regions devoid of
atoms) - Bubbles (voids stabilized by
filled gases, such as He)
How can the temperature affect the level of radiation damage?
- The higher temperature, the higher the mobilities of defects
- Effect of neutron irradiation
Destroys crystal structure and affects chemical bonds,
Creates point defects, He and H, clusters, modifies
microstructure and leads to hardening/embrittlement.
Causes degradation of physical and mechanical properties.
what are the examples of radiation induces material performance degradation?
- Radiation hardening and
embrittlement (<0.4 TM, >0.1 dpa) - Phase instabilities from radiation induced precipitation (0.3-0.6 TM, >10dpa)
- Irradiation creep (<0.45 TM, >10 dpa)
- Volumetric swelling from void
formation (0.3-0.6 TM, >10 dpa) - High temperature He embrittlement(>0.5 TM, >10 dpa)
What are the three main steps of the evolution of defect structures ate different irradiation temperature?
untested??
What are the effects of irradiation hardening on the material?
Irradiation hardening:
Increase in yield strength
Increase in the ultimate tensile strength
Decrease in rate of work hardening
Reduction in uniform and total elongations
As the strength increases the toughness decreases.
What are the effects of irradiation embrittlement on the material?
Irradiation embrittlement
bcc alloys
Increase in ductile-brittle transition
temperature (DBTT)
Decrease of upper-shelf energy
fcc alloys
Helium embrittlement
the irradiated material becomes more brittle.
What is nuclear transmutation?
Conversion of one chemical element or isotope into another e.g a neutron and a parent nucleus merge for a daughter nucleus and alpha particle(helium).
He as transmutation product
Insoluable in a metal lattice
Void swelling
He embrittlement
What are the effects of void swelling on the material? and how can it be improved?
Diffusing vacancies meet and form pores (voids) at 0.3-0.6 TM
Vacancy accumulation= unacceptable volumetric expansion
Can be improved either through the composition (bcc steels are better than fcc steels) or microstructure modification (grain boundaries, dislocation or dispersoids)
What are material challenges in advanced nuclear reactors?
- Requirement for higher temperature materials with adequate radiation resistance.
- Long term stability of both microstructure and mechanical
properties.
Fusion functions at much higher temperatures then original fission reactors. The cost per kg however is much more expensive for the future reactor designs than the original.
What are the 2 main types of nuclear energy production?
Fission(reliable supplier of electricity and next generation reactor development) and Fusion( potentially attractive but technically challenging = higher energy output and is under development)
What are the main components of a nuclear power plant to support how it works?
There is heat produced from fission which heats a vat of water to produce steam. This steam passes through to turn a turbine which is connected to a generator and turns this. The generator will then produce electricity.
What are the equations of efficiency for a heat engine and what is a creep a function of?
efficiency ref pg 12
creep(AKA strain) = f( strees, temperature, time)
What is nuclear fission?
- Fuel is consumed during fission
- Fuel is changing composition during irradiation
- Neutrons are consumed and created during fission
A neutron reacts with a uranium isotope to produce fission products, neutrons and energy.
What are the 5 main components of a nuclear power reactor?
- A designated fuel
- A reactor zone where fission can occur
- A cooling system and circuit to extract heat energy
- A moderator to slow or absorb the neutrons and control the rate of fission
- A containment system
What are 4 possible damages and complications that must be taken into account for nuclear reactor design?
- Safety features because of the radiation of neutrons, particles and
beta-rays, - Possible radiation damage to the constructional material leading to weakness,
- Environmental damage through leakage of radioactive waste which may be gases solids or dissolved species, hence the need for good fuel cans and heat exchangers,
- Closure at the end of its life, ie, amortization – cost and ‘blot on landscape’.
